1. Field of the Invention
The present invention relates to an intake manifold for distributing air into a plurality of cylinders of an engine and, more particularly, to an intake manifold having a gas passage for returning gas such as a blowby gas (a PCV gas) having leaked out of the engine into a crankcase to the engine.
2. Description of Related Art
There is heretofore an intake manifold of this type, an example of which is disclosed in Japanese unexamined patent publication No. 2002-322953. This intake device includes a partition wall in an air connector provided in an intake manifold, the partition wall being arranged in parallel to a direction of an air flow, thereby forming upper and lower passages in order to split an air flow into two flows, upper and lower. The partition wall is partially formed with a through hole which allows communication between the upper and lower passages. The air connector is provided with a gas intake pipe having one end open to the through hole and the other end extending to the outside of the air connector. Through this gas intake pipe, PCV gas or the like is delivered into the intake manifold. In this device, the PCV gas delivered through the gas intake pipe is split at the through hole into the upper and lower passages and then distributed from the air connector into each runner (branch pipe).
In the intake device disclosed in the '953 publication, the gas introduced through the gas intake pipe is split into two flows above and below the partition wall. However, the gas is subsequently allowed to flow freely in each passage and further the inlet ports of the plurality of branch pipes are located at different distances from the air connector. Thus, the gas could not be readily equally distributed into the branch pipes.
In order to meet a demand for weight reduction and size reduction of an engine system, a lightweight and compact intake manifold has been recently required. Conceivably, the intake manifold could be molded of resin to reduce weight. As for such resin-molded intake manifold, however, the above '953 publication suggests no concrete technique for integrally forming the gas path or passage for PCV gas or the like.